The present invention relates to a device for transporting and placing a bridge of an offshore oil rig for sea operation onto a floating or stationary structure.
Generally, offshore oil rigs for sea operation comprise a bridge carrying operating equipment and living space. The bridge is supported by a stationary structure, such as tubular pillars or legs pushed into the marine soil or resting thereon with the help of shoes or on a floating structure, such as a column or assembly of columns, for example.
The transport and placement of this type of platform on the operation site can be done in several ways.
The first method consists of transporting the bridge using at least one barge and then, using a crane, lifting the bridge and placing it on the mounting structure.
The second method consists of bringing the floating platform assembly to the operation site and attaching the platform on the site. In case of a stationary structure formed by telescopic legs, the legs are lowered until they come into contact with the sea bottom, then, bearing on the legs, the bridge is hoisted above sea level up to an altitude that puts it out of reach of the highest waves.
The third transport and placement method consists first of attaching the stationary or floating structure to the operation site and conveying the bridge of the rig from the assembly worksite to the site using at least one transport barge and, when the dimensions of the bridge are large or when the mounting structure does not make it possible to position the barge, the transport is then done using two parallel floating transport barges.
The bridge of the platform is therefore placed on the two barges, which are distanced from each other, to allow these barges to pass on either side of the floating or stationary mounting structure in order to install the bridge there.
After towing the assembly formed by the barges and the bridge, from the assembly worksite to the operation site, the bridge is positioned vertically relative to the mounting structure and the load of the bridge is transferred from the barges onto said structure.
The transfer of the bridge from the barges onto the mounting structure can be done in two ways, depending on the manner in which the bridge is carried by the barges.
The bridge of the oil rig is either placed on shims positioned on each barge or placed on a set of rams positioned on each barge.
In the first case, the passage of the bridge from the barges towards the mounting structure is done by ballasting the barges or deballasting the support column in the case of a floating structure.
In the second case, the passage from the mounting structure is done by actuating the rams to lift the bridge relative to the barges and the assembly is positioned above the mounting structure, then the rams are actuated to lower the bridge again and transfer the load of the bridge onto the mounting structure.
However, the problem that arises during installation of the bridge using barges on a slightly bumpy sea, lies in the movement of said barges relative to the bridge when the bridge is transferred from said barges onto the mounting structure.
To resolve this problem, it is known to install, between each barge and the bridge, brackets before towing the bridge and in a calm zone, such as close to the dock of the bridge assembly worksite. These brackets make it possible to rigidify the connection between the bridge and the barges.
When the assembly is on the operation site and the bridge is positioned near the mounting structure, the brackets can be cut away or removed before lifting the load of the bridge from the barges to the mounting structure.
The brackets are removed before or during the transfer of the bridge load from the barges to the floating structure. But in that case, the barges are free to roll, which causes additional stresses on the supports of the barges carrying the bridge.
The invention aims to resolve these drawbacks.